Position detector for moving vehicle

ABSTRACT

A position detecting system for a moving vehicle wherein a position of the moving vehicle is detected on the basis of received beam signals from light-emitting means disposed at at least four reference points and positional informations of the respective reference points, comprising a means for detecting the azimuth of each light-emitting means with respect to the moving vehicle, a means for predicting the direction of the light-emitting means to be detected in the next scanning on the basis of the azimuths detected, a means for calculating the position of the moving vehicle on the basis of the detected azimuths if the detected position of the light-emitting means is in the predicted direction, and a means for calculating the azimuth of the undetected light-emitting means on the basis of the positions of the remaining light-emitting means if the detected position of the light-emitting means is out of the predicted direction, and for predicting the azimuth at which the undetected light-emitting means is to be detected in the next scanning.

BACKGROUND OF THE INVENTION

1. Field of the invention

The present invention relates to a position detector for a movingvehicle, and more particularly to a position detector for traveling amoving automobile, an unmanned mobile and carrying device in a factory,or a steering vehicle for use in agriculture, civil engineeringmachinery and the like along a predetermined traveling course.

2. Description of the Prior Art

Heretofore, as a system for detecting a present position of a movingbody such as the moving vehicles as described above, there has beenproposed a system provided with a means for scanning a light beamemitted from a moving body in the circumferential direction or everyazimuthal direction centering around the moving body, light-reflectingmeans for reflecting to return the light beam in the direction ofincident light and secured at at least three positions apart from themoving body, and a beam receiver means for receiving light reflectedfrom the light-reflecting means (the Japanese Pat. Laid-open No.67476/1984).

In the above mentioned prior art, differential azimuths betweenadjoining two of three light-reflecting means centering around themoving body are detected on the basis of received beam output of thelight-receiving means, then a position of the moving body is operatedbased on the detected differential azimuths and positional informationof the light-reflecting means which have been previously set.

In such a prior art system, if a moving body having a beam-receivingmeans mounted thereon is positioned in the neighborhood of the centralportion of a triangle with the respective light-reflecting means securedat the three positions as the vertexes, the position of the moving bodycan be detected with a fairly high precision. However, there was aproblem that, in a position apart from the neighborhood of the centralportion of the triangle, it was difficult to obtain a high measuringprecision.

As a countermeasure therefor, for instance, as described in U.S. patentapplication No. 413,934 (Japanese patent application No. 262191/1985) orthe Japanese patent Laid-open No. 14114/1985 or No. 15508/1985, therehave been proposed methods for measuring the position of a moving bodywherein reference points are set on the vertexes of a quadranglesurrounding the area in which the moving body travels, optimum threereference points of the four reference points with which a highmeasuring precision can be expected are selected, and the positionaldetection of the moving body is performed on the basis of the positionalinformation of the selected three reference points and the azimuths ofthe reference points viewed from the moving body.

Furthermore, U.S. patent application No. 413,935 (Japanese applicationSer. No. 63-257912) discloses a system for detecting the position andadvance direction of a moving body (hereinafter referred to as "movingvehicle") in which differential azimuths defined between two referencepoints disposed at diagonal positions among four reference points viewedfrom the moving vehicle are calculated on the basis of the azimuthsdefined by the four reference points with respect to the advancedirection of the moving vehicle, and then the position and the advancedirection of the moving vehicle are detected based on the azimuthsdefined by the four reference points, the differential azimuth definedbetween two reference points, and obtained positional information of therespective reference points.

In the above described system, however, there have been a case where alight beam cannot be projected on light-reflecting means disposed at thereference points because of tilt or vibration of the moving vehicleand/or a case where a light-receiving means installed on the movingvehicle receives light reflected from an object other than the abovedescribed light-reflecting means. If the reflected light of light beamcannot be positively received by the light-receiving means, a positionof the moving vehicle is erroneously calculated, and as a result themoving vehicle cannot be allowed to travel along a predetermined course.

There is described in U.S. patent application No. 349,184 (US89A:Japanese patent application No. 63-262192) a detecting system which isso constructed that an azimuth of the reference point missed is sopresumed in case of missing the reference points due to an inablility toreceive reflected light, and a position of the moving vehicle is thencalculated by using the azimuth angle of the presumed reference point.

In the above technique wherein a position of a moving vehicle iscalculated by presuming the azimuth of a reference point, errors as aresult of presumptions are accumulated with the increase of the missingnumber of times, so that accurate positional detection may not beattained. For this reason, it has been also proposed such a constructionthat, for example, travel of the moving vehicle is allowed to stop whenthe counted missing number of times exceeds a predetermined number oftimes. In this respect, however, most of the cases in which a referencepoint is missed are tentative phenomena. Accordingly, if a movingvehicle is allowed to frequently stop to interrupt its working becauseof such tentative phenomena, the working efficiency decreases.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a position-detectingsystem for a moving vehicle in which the working efficiency of themoving vehicle can be increased by reducing the error in estimating theposition of a missing reference point, and enabling reduction of thefrequency of interruptions during the traveling of the moving vehicledue to missing of a reference point.

The present invention is characterized in such a construction that in aposition detecting system for a moving vehicle wherein a position of themoving vehicle is detected on the basis of received beam signals derivedfrom the light beam emitted from light-emitting means disposed at atleast four reference points positioned apart from the moving vehicle andpositional informations of the respective reference points, comprising ameans for detecting the azimuth of each light-emitting means withrespect to the moving vehicle on the basis of light receiving intervalsin the light-receiving means, a means for predicting the direction ofthe light-emitting means to be detected in the next scanning on thebasis of the azimuths detected in the azimuth detecting means, a meansfor calculating the position of the moving vehicle on the basis of thedetected azimuths if the detected position of the light-emitting meansis in the direction predicted in the predicting means, and a means forcalculating the azimuth of the undetected light-emitting means on thebasis of the positions of the remaining light-emitting means other thanthe undetected light-emitting means if the detected position of thelight-emitting means is out of the direction predicted in the predictingmeans, and for predicting the azimuth at which the undetectedlight-emitting means is to be detected in the next scanning.

In the present invention having the above described construction, if oneof the four reference points is not detected, the azimuth of theundetected one reference point can be calculated on the basis of theazimuths of the remaining three reference points other than theundetected reference point. Accordingly, the azimuth of the undetectedone reference point can be calculated on the basis of the definitepositions of the three reference points rather than by mere estimation,so that an accurate prediction can be made for the position at whichsaid one reference point is to be detected in the next scanning.

As a result, the error in the positional prediction is very small, evenif the reference point disposed at one reference point has been missed,and the positional detection of the moving vehicle can be performed withvery small accumulation errors even in consecutive missings, so that therunning with no practical hindrance can be continued withoutinterrupting the traveling of the moving vehicle even if the missing ofa particular reference point successively occurs.

BRIEF DESCRIPTION OF THE DRAWING

FIGS. 1 and 2 are block diagrams showing an embodiment of the presentinvention;

FIG. 3 constituting FIGS. 3A-3B is a flowchart of a steering control;

FIG. 4 constituting FIGS. 4A-4E is a flowchart of a processing fordiscriminating reference points;

FIG. 5 is a flowchart of a reverse calculation of a missing referencepoint;

FIG. 6 constituting FIGS. 6A-6D is a flowchart of a reference pointmissing processing;

FIG. 7 constituting FIGS. 7A-7D is a flowchart of a processing fordetermining azimuths;

FIGS. 8 and 9 are explanatory graphical representations of therelationship between the advance direction of the moving vehicle andazimuths of the reference points and differential azimuths;

FIG. 10 is a graphical representation showing an arrangement of atraveling course of the moving vehicle and reflectors;

FIG. 11 is an explanatory representation of the azimuth of a referencepoint; and

FIG. 12 is a perspective view showing an arrangement of the movingvehicle and reflectors.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the present invention will be described hereinbelow byreferring to the accompanying drawings. FIG. 12 is a perspective viewshowing a state of arrangement in respect of a moving vehicle carryingthe control system according to the present invention and a plurality oflight reflectors disposed in an area in which the moving vehicletravels.

In FIG. 12, the moving vehicle 1 is one for use in agricultural workingsuch as a lawn mower and the like. A rotating table 4 driven by a motor5 is mounted on the upper part of the moving vehicle 1. The rotatingtable 4 mounts a beam source 2 for emitting light beam 2E and a beamreceiver 3 for receiving light 2R reflected by each of the reflectors6a-6d for reflecting the light beam 2E. The beam source 2 is providedwith a light beam emitting means (light-emitting diode) and the beamreceiver 3 is provided with a means for receiving incident light toconvert it into an electrical signal (photo-diode) (both of them are notshown). Furthermore a rotary encoder 7 is disposed so as to beinterlocked with a drive shaft of the rotating table 4, so that whenpulses output from the rotary encoder 7 are counted, a turning angle ofthe rotating table 4 can be detected.

The reflectors 6a-6d are located around a working area of the movingvehicle 1. Each of the reflectors 6a-6d has a reflection surfacereflecting incident light in the incident direction and for thispurpose, a so-called corner cube prism which has been conventionallyavailable on the market and the like may be used.

Next, the construction of the control system in the present embodimentwill be described in accordance with the block diagrams of FIGS. 1 and 2wherein the light beam 2E emitted from the beam source 2 is scanned in arotating direction of the rotating table 4 and the light beam 2E isreflected by one of the reflectors 6a-6d. The light beam 2R reflected bythe one of the reflectors 6a-6d is introduced into the beam receiver 3.

In a counter 9, the number of pulses output from the rotary encoder 7 iscounted in accordance with rotation of the rotating table 4. The countvalue of the pulses is transferred to a discrimination processing means11 in every reception of the reflected light beam in the beam receiver3. In the discrimination processing means 11, an azimuth of eachreflector 6 with respect to the advance direction of the moving vehicle1 is calculated on the basis of the count value of the pulsestransferred in every reception of the reflected light beam.

Actual azimuths detected by the discrimination processing means 11 and apresumed azimuth in case where a reference point is missed (the detailsof such presumed azimuth will be described hereinbelow) are inputted toa diagonal differential azimuth operating means 37 and a firstposition-advance direction operating means (hereinafter referred tosimply as "first operating means") 34 as well as an adjoiningdifferential azimuth operating means 10 and a second position-advancedirection operating means (hereinafter referred to simply as "secondoperating means ") 13 through a switching means 36.

The switching means 36 is switched in response to the presence of areference point-missing signal "d" output from the discriminationprocessing means 11. In FIG. 2, such a situation in which the signal "d"is output, and as a result the switching means 36 is switched to theside of the adjoining differential azimuth operating means 10 as well asthe second operating means 13 is illustrated.

In the diagonal differential azimuth operating means 37, differentialazimuths defined between each pair of the reflectors 6 disposed atdiagonal positions, respectively, among the reflectors 6 placed at fourpositions viewed from the moving vehicle 1 are operated. In the firstoperating means 34, the coordinates of a current position of the movingvehicle 1 are calculated on the basis of the above describeddifferential azimuths and at the same time, the advance direction of themoving vehicle 1 is calculated on the basis of the azimuths of the fourreflectors 6.

Furthermore, differential azimuths defined between two reflectors 6adjoining with each other among the three reflectors out of four areoperated in the adjoining differential azimuth operating means 10. Inthe second operating means 13, coordinates of a current position of themoving vehicle 1 are calculated on the basis of the above differentialazimuths and the advance direction of the moving vehicle 1 issimultaneously calculated based on the azimuths defined by the threereflectors 6 out of four. The three reflectors 6 mentioned above meanthe three reflectors 6 other than the single reflector 6 disposed at thereference point missed.

The results of the operations in the first operation means 34 and thethe second operation means 13 are inputted to a comparing means 25. Inthe comparing means 25, data indicating a traveling course set in atraveling course setting means 16 are compared with the coordinates andthe advance direction of the moving vehicle 1 obtained in the firstoperation means 34 or the the second operating means 13.

The comparison results are supplied to steering means 14, and a steeringmotor (M) 35 connected to front wheels 17 of the moving vehicle isdriven on the basis of the above-mentioned comparative results. An angleof steering for the front wheels 17 driven by the steering motor 35 isdetected by means of a steering angle sensor 15 mounted on the frontwheels of the moving vehicle 1, and fed back to the steering means 14.

A driving means 18 controls starting and stopping of an engine 19 aswell as operation of a clutch 20 for transmitting the power of theengine 19 to rear wheels 21.

Incidentially, of the structural elements shown in FIG. 2, the portionsurrounded by a chain line may be constructed by a microcomputer.

Next, the detailed construction of the discrimination processing means11 will be described hereinbelow. In the discriminating processing means11, the azimuths are found and at the same time, discriminating andmissing processings for the light beam reflectors 6 are carried out onthe basis of the azimuths.

Referring to FIG. 1, the azimuths of the respective reflectors 6 areoperated with respect to the advance direction of the moving vehicle 1on the basis of a count value of the counter 9 in the azimuth operatingmeans 23. In an azimuth storing means 35, one azimuth for a certainreflector 6 which is detected in the last cycle as well as anotherazimuth for the same reflector 6 which has been detected in thebefore-last cycle are stored.

More specifically, a pair of azimuths which were detected in the lastand the before-last detection cycles are stored in the storing means 35in each respect of the azimuths θa-θd for the reflectors 6a-6d locatedat reference points A-D, respectively. Based on the last azimuth, apredictive azimuth which is to be detected in respect of some particularreflector 6 in the next step is operated in a predictive azimuthoperating means 26 wherein the predictive azimuth has a predeterminedrange.

In the discrimination means 24, the predictive azimuth is compared withthe actual azimuth which has been operated by the azimuth operatingmeans 23.

A pole counter 27 is constructed in such that each of count values isrenewed by such count value which is allowed to correspond to each ofthe reflectors 6 disposed at the reference points A, B, C and D in everydetection thereof. Then, the count values of the pole counter 27 areinputted to the discrimination means 24, and compared with predeterminednumerical values, respectively, which have been set in thediscrimination means 24.

In accordance with a comparative result of the predictive azimuth withthe actual azimuth in the discrimination means 24 as well as acomparative result of the count values in the pole counter 27 with thepredetermined numerical values, it is judged whether or not a signaldetected in the beam receiver 3 is a real detection signal of thereflected light from the predictive reflector 6.

In the case when the reflected light from the expected reflector 6 isdetected, a discrimination signal is output "a" from the discriminationmeans 24, and as a result the actual azimuth is inputted to the diagonaldifferential azimuth operating means 37 and the first operating means 34or the adjoining differential azimuth operating means 10 and the secondoperating means 13 through the switching means 36.

At the same time, in the azimuth storing means 35, the last azimuth isrenewed by the latest detected azimuth, and the before-last azimuth isrenewed by the last azimuth.

On the contrary, when it is judged that the detection signal in the beamreceiver 3 is one from the reflector 6 other than the expected reflector6, the count value in a missing number counter 30 is increased by asignal "b" as a result of having missed the expected reflector 6.

In the case when two of the expected reflectors 6 have been seriallymissed, a count value is renewed in a plural missing number counter 31in response to a signal "c". When the detection signal in the beamreceiver 3 is a signal from something other than the reflectors 6, thesignal is processed as noise, and a position of the moving vehicle 1 atthe time of receiving the noise and an azimuth of a noise source viewedfrom the moving vehicle 1 are stored in a noise storing means 29.

The count value in the counter 30 is compared with a first thresholdvalue T1 in a first comparing means 32, whilst the count value in thecounter 31 is compared with a second threshold value T2 in a secondcomparing means 33. In the case where the count values of the missingnumber are less than the threshold values T1 and T2 in both thecomparing means 32 and 33, a processing for estimating an azimuth of themissing reflector 6 is effected in an azimuth estimating means 28 on thebasis of the last and the before-last azimuthes stored in the azimuthstoring means 35.

After being estimated by the azimuth estimating means 28, the last andthe before-last azimuths in the azimuth storing means are renewed.

Furthermore, when the missing number of times exceeds the thresholdvalue T1, based on the last azimuths of the three reflectors 6 otherthan the missing reflector 6, which are stored in the azimuth storingmeans 35, the azimuth of the missing reflector 6 is calculated in themissing reference point reverse calculation means 34. The calculatedazimuth is stored in the azimuth storing means 35 as the last azimuth ofthe missing reflector 6. Also, the calculated azimuth is inputted to thepredictive azimuth operation means 26 where, based on this azimuth, apredictive azimuth is calculated at which the missing reflector 6 is tobe detected in the next scanning.

Furthermore, when the missing number of times exceeds the thresholdvalue T1, the signal "d" is output to the switching means 36, wherebythe switching means 36 is switched to the situation illustrated in FIG.1.

On one hand, when plural missing number of times exceed the thresholdvalue T2, a signal "e" is output to the driving means 18 to stop travelof the moving vehicle 1.

Since missing of two reference points is more seriously affected thanmissing of one reference point as to precision in positional detectionof the moving vehicle 1, less number of times than that of the thresholdvalue T1 is set as the threshold value T2. It is arranged in such thatif adjoining two reference points are missed, the moving vehicle 1 isstopped at once at the time when the plural missing number of timesexceeds the threshold value T2.

On the other hand, in case of missing one reference point, it isarranged in such that the position and the advance direction of themoving vehicle 1 are operated on the basis of positions and azimuths ofthe reflectors 6 disposed at three reference points except the missingreference point when the missing number of times exceeds the thresholdvalue T1.

When it is judged by the discrimination means 24 that light reflectedfrom the expected reflector 6 is received, both of the missing numbercounter 30 and the plural missing number counter 31 are reset.

A value in the pole counter 27 is renewed in the case when it is judgedby the discrimination means 24 that the expected reflector 6 has beennormally detected as well as the case when missing processing has beencompleted, or the azimuth has been calculated in the reverse calculationmeans 12 and azimuth estimating means 28.

FIGS. 8 and 9 are explanatory graphical representations each showing theposition T of the moving vehicle 1 and that of the reflector 6 in acoordinate system for indicating a working area of the moving vehicle 1.

In FIG. 8, disposed positions of the reflectors 6a-6d are indicated bypoints A-D (hereinafter referred to as "reference points A, B, C andD"). The positions of the reference points are represented by an x-ycoordinate system. The current position of the moving vehicle 1 is T(x,y) and advance direction with respect to the x-axis is θf.

Azimuths of the reference points A, B, C and D with respect to theadvance direction of the moving vehicle 1 are designated by θa, θb, θcand θd, respectively, and differential azimuths defined betweenreference points positioned at the respective diagonal positions aredesignated by φ1 and φ2, respectively.

FIG. 9 shows relationships between the remaining three reference pointsA, B and C in case of missing one reference point (reference point D inthe same figure) and the moving vehicle 1, respectively, in whichreference characters θa, θb and θc denote the azimuths of the respectivereference points A, B and C with respect to the advance direction of themoving vehicle 1, and α and β denote differential azimuths definedbetween adjoining reference points A and B as well as B and C,respectively. θ1 and θ2 are angles of a straight line passing throughthe current position T of the moving vehicle 1 and the reference pointC, and a straight line passing through the current position T of themoving vehicle 1 and the missing reference point D, respectively.

A formula for calculating a position T (x, y) and an advance directionOf of the moving vehicle 1 based on the above described azimuths θa, θb,θc and θd, as well as the differential azimuths φ1 and φ2 is stored inthe first operating means 34, whilst another formula for calculating aposition T (x, y) and an advance direction θf of the moving vehicle 1based on the above described azimuths θa, θb and θc as well as thedifferential azimuths α and β is stored in the second operating means13. An example of the formula to be stored in the first operating means34 and that of the second operating means 13 are described in detail inU.S. patent application Ser. No. 413,935 (Japanese patent applicationSer. No. 63-257912) as well as U.S. patent application Ser. Nos. 344,574and 362,630, (now U.S. Pat. No. 4,947,324) respectively. Accordingly,the explanation therefor will be omitted herein.

Next, steering control for the moving vehicle 1 based on the positionalinformation of the moving vehicle 1 calculated in accordance with theabove procedure will be described hereinbelow. FIG. 10 is a schematicdiagram showing a traveling course of the moving vehicle 1 and thecoordinates of the reflectors 6, and FIG. 3 is a flowchart illustratinga procedure for steering control.

In FIG. 10, points A, B, C and D indicate positions at which thereflectors 6a-6d are disposed, and the current position T and theworking area 22 of the moving vehicle 1 are represented on a coordinatesystem wherein the point B is fixed as the origin, and a straight lineextending between the points B and C is defined as the x-axis. (Xret,Yret) indicate coordinates of a returning position R of the movingvehicle 1, and the working area 22 is a quadrilateral region includingfour apexes of the points represented by four coordinates (Xst, Yst),(Xst, Ye), (Xe, Yst) and (Xe, Ye). In this case, the current position ofthe moving vehicle 1 is represented by T(Xp, Yp).

For the simple explanation, while an example wherein four sides of theworking area 22 are parallel to x- or y-axes is shown in FIG. 10, otherdirections and/or shapes of the working area may be selected so far asthe points A-D are disposed around the working area 22.

In accordance with the flowchart shown in FIG. 3, a control procedurewill be described hereinbelow in which it is assumed that the movingvehicle 1 reciprocates in parallel to the y-axis as in the travelinglocus of FIG. 10, and the pitch therefor is L.

First of all, in step S1, the moving vehicle 1 is transferred by meansof, for example, radio control from a point R to a position whereworking is to be started.

In step S2, the beam emitter 2 and the beam receiver 3 are rotated whilestopping the moving vehicle 1 to detect the respective reference pointsA, B, C and D, and at the same time azimuths of the respective referencepoints viewed from the moving vehicle 1 are stored in the storing means35.

In step S3, Xst is set as an X-coordinate Xn for a traveling coursethereby to fix the traveling course.

Traveling of the moving vehicle 1 is started in step S4.

It is judged in step S5 whether or not reflected light from anyreference point is received by the beam receiver 3. The step 5 isrepeated until the reflected light is detected. When detected thereflected light, the operation proceeds to step S6, and a subroutineprocess for discriminating reference points which will be describedhereinafter is carried out.

In step S7, it is judged whether a reference point has been missed ornot dependent upon the reference point-missing signal d output from thefirst comparing means 32.

If the judgment in the step S7 is "NO", i.e. in the case where it isjudged that any one reference point among the reference points disposedat four positions has not been successively missed over a predeterminednumber of times (threshold value T1), the procedure proceeds to step S8where the position and the advance direction of the moving vehicle 1 areoperated on the basis of the four reference points in the firstoperating means 34.

If the judgment in the step S7 is "YES", i.e. in the case where it isjudged that a particular one reference point among the reference pointsdisposed at four positions has been successively missed over apredetermined number of times (threshold value T1), the procedureproceeds to step S9 where the position and the advance direction of themoving vehicle 1 are operated on the basis of the remaining threereference points in the second operating means 13.

In step S10, the azimuth of the reference point which has beensuccessively missed over a preset number of times is reverselycalculated on the basis of the azumuths of the three reference pointsother than the missed reference point. The calculation formulas for thereverse operation will be described later.

In step S11, a deviation amount of the traveling course (ΔX=Xp-Xn, Δθf)is operated, and a steering angle is controlled in step S12 by thesteering means 14 in response to the amount of deviation calculated.

In step S13, it is judged that either the moving vehicle 1 travelstowards the direction going away from the origin (forward direction) orthe direction approaching the origin (reverse direction) in the y-axialdirection.

In case of forward direction, it is judged whether one stroke has beenfinished (Yp>Ye) or not in step S14, whilst in case of reversedirection, it is judged whether one stroke has been finished (Yp<Yst) ornot in step S14. When it is judged that such one stroke has not beenfinished in either step S14 or step S15, processing returns to step S5.

In case where it is judged that such one stroke has been finished ineither step S14 or S15, it is judged in the following step S16 whetherall the strokes have been finished (Xp>Xe) or not.

When all strokes have not been finished, the procedure shifts from stepS16 to step S17 to effect U-turn control of the moving vehicle 1. U-turncontrol is carried out in accordance with a different method from theone for steering control in a straight traveling course which iseffected according to processing steps S11 and S12 wherein thepositional information of the moving vehicle 1 operated by the first orthe second operating means 34 or 13 is fed back to the steering means14.

More specifically, it is adapted that the vehicle 1 is traveled whilefixing a steering angle thereof at a predetermined angle in a turningcourse, and the moving vehicle returns to steering control in a straighttraveling course which is effected in accordance with processings ofsteps S5-S12 at the time when at least one of azimuths of the respectivereflectors 6 viewed from the vehicle 1 substantially falls in apredetermined range of corresponding azimuth. The details of U-turncontrol for traveling the moving vehicle along the turning course isdescribed in detail in the U.S. patent application Ser. No. 362,630, nowU.S. Pat. No. 4,947,324.

In step S18, a pitch L is added to Xn thereby operating (Xn+L) and thefollowing traveling course is set. When set the following travelingcourse, the procedure returns to step S5 and the above describedprocessings are repeated.

When all strokes are completed, the moving vehicle returns to the returnposition R(Xret, Yret) in step S18, and the travel thereof stops in stepS20E.

Next, the processing for discriminating reference points in the step S6will be described hereinbelow.

In the present embodiment, measures for discriminating reference pointsare constructed in such that the respective reference points A-D areallowed to correlate with count values of the pole counter 27, forexample, reference points A, B, C and D are allowed to correlate withcount value 1, 2, 3 and 4, respectively, whereby the respectivereference points are discriminated from one another. More specifically,the pole counter 27 outputs the count values 1, 2, 3 and 4 in that orderin every detection of the reflected light 2R by the beam receiver 3 andthe reference points can be discriminated by supervising the countvalues. For instance, when the light beam signal from the referencepoint B is received, the count value in the pole counter 27 should be"1" because the reference point detected immediately before thedetection of the reference point B is A.

Accordingly, if the count value in the pole counter 27 is "1" when alight beam signal is detected within the predictive range in which anexpected reference point (B in this case) is to be detected, it can bejudged that the expected reference point has been normally detected.

In the case when a reference point has been lost, or reflected light isreceived from an object other than the reference points, the referencepoints do not correlate with the count values. As the result, it can berecognized that a reference point has been lost, or reflected light isreceived from some object other than the reference points. Accordingly,in the processings for discriminating reference points shown in aflowchart of FIG. 4, it is assumed that only the light detected within apredicted azimuth range is normal reflected light from an expectedreference point. Under this assumption, in the processings shown in FIG.4, it is judged whether or not the count values output from the polecounter 27 correspond to the reference points, and based on the resultof the judgement it is concluded whether or not the expected referencepoints have been normally detected after all.

As a result of the above judgment, the position is continuously detectedin accordance with the undermentioned reference point-missing processingwhen it is judged that a reference point has been missed or/and it isjudged that light beam had been received from any reflecting objectother than the reference points. When the number of times in missingsuccessively particular one reference point exceeds the predeterminednumber of times, steering control of the moving vehicle 1 is continuedon the basis of the informations of the other three reference pointsthan the aforesaid particular missing reference point.

Moreover, when one particular reference point has been successivelymissed over a preset number of times, the azimuth of the missingreference point is calculated by a reverse operation based on theazimuths of the remaining three reference points other than the missingreference point, and an azimuth range is obtained in which thatreference point is to be detected in the next scanning based on theazimuth calculated by a reverse operation.

When the number of times in missing successively a plurality ofreference points exceeds the predetermined number of times, travel ofthe moving vehicle 1 is adapted to stop.

Next, an example of a method for presuming azimuths of reference pointsin order to judge that the light detected is the one from a prescribedreference point will be described hereinbelow in conjunction with thereference point A.

FIG. 11 is a diagram showing changes in azimuth of the reference point Aviewed from the moving vehicle 1 with the travel thereof wherein it isassumed that the azimuth at just previous detection cycle time when themoving vehicle 1 exists at the point m1 is θan-1, and the azimuth at thecurrent detection cycle time when the moving vehicle 1 exists at thepoint m2 is θan. In these circumstances, it is predicted that theazimuth at the next detection cycle time when the moving vehicle 1 isexpected to exist at the point m3 is (θan±θK) where θK is a fixed value.In this case, the fixed value θK is determined on the basis of an angle{θan-(θan-1)} which is found experimentally.

According to the experiments by the present inventors, since{θan-(θan-1)} falls within a range of about several degrees except forthe case where the moving vehicle 1 is in the turning course, the fixedvalue θK is set to 3 degrees in the present embodiment. However, thefixed value θK is switched to a larger preset value than that instraight travel of the moving vehicle 1, because changes in the azimuthmust be abrupt during turning of the moving vehicle 1. In the presentembodiment, the fixed value θK during turning of the moving vehicle 1 isset to 30 degrees. Either θK may be set as such a fixed value which isbased on the experiment as mentioned above, or a difference between twoazimuths which were detected at the latest and the second latestdetection cycle times and have been stored in the azimuth storing means35 may be set as the value θK.

The method for predicting the azimuth of the reference point A has beendescribed with refering to FIG. 11, and the azimuths of the otherreference points B-D are similarly predicted.

The processing for discriminating reference points will be explained inaccordance with the flowchart shown in FIG. 4 wherein an azimuth of anobject, by which light is reflected, with respect to the advancedirection of the moving vehicle 1 which was calculated on the basis ofthe latest beam signal received is read in as θx in step S61.

In step S62, it is judged whether or not θx is within a range of(θan±θK). If the judgment in the step S62 is "YES", the received beamsignal is assumed to be a reflected signal from the reference point Aand the operation proceeds to step S67.

In the step S67, it is judged whether or not the count value in the polecounter 27 is a value "4" corresponding to the reference point D whichis to be detected before the detection of the reference point A. If thecounted value is "4", such assumption made in the step S62 that "thereceived beam signal is a reflected signal from the reference point A"is considered to be right, so that the processes in steps S68 and S69are performed, that is, the azimuth θa of the reference point A viewedfrom the moving vehicle 1 is determined. The details of the processingfor determining the azimuth angle θa will be described hereunder inconjunction with FIG. 6A.

In the step S69, a count value in the pole counter 27 is set to be "1"corresponding to the reference point A. After that, the operation isreturned to the step S7 in the main routine (FIG. 3).

On the other hand, if it is judged in the step S67 that the count valuein the pole counter 27 is not "4", the operation proceeds to step S70where it is judged whether or not the count value in the pole counter 27is "3". If the judgment in the step S70 is "YES", it is judged that thereference point D has been lost immediately before, so that theoperation proceeds to step S71 where the missing of the reference pointD is processed.

The details of the processing for the missing of the reference point Dwill be shown in FIG. 5D. After completing the processing for themissing of the reference point D, the operation proceeds to step S72.

In the step S72, it is judged whether or not a missing number of times ILostD for the reference point D exceeds the threshold value T1.

In the judgment in the step S72, when the missing number of times ILostD for the reference point D does not exceed the threshold value T1,the operation proceeds to the step S73 where it is judged whether or notthe missing number of times I LostBD which shows that two adjoiningreference points B and D have been lost exceeds the threshold value T2.When it does not exceed T2, the operation proceeds to the step S68. Whenit exceeds the threshold value T2, the operation proceeds to step S135and the clutch 20 in the moving vehicle 1 is disconnected, the engine 19is stopped, and a fail lamp is lit continuously or intermittently.

Moreover, in the step S72, when it is judged that the missing number oftimes for the reference point D, I LostD, has exceeded the thresholdvalue T1, the procedure shifts to step S74 where "1" is set in areference point D missing flag, and then the procedure proceeds to stepS73.

When the judgment in the step S70 is "NO", the procedure proceeds tostep S75 where it is judged whether the count value in the pole counter27 is "2" or not.

If the judgement in the step S75 is "YES", it is considered that thereference points C and D have been missed, then, the procedure proceedsto step S76 where a reference point C missing processing similar to thereference point D missing processing is effected.

In step S77, it is judged whether or not the missing number of times forthe reference point C, I LostC, exceeds the threshold value T1. In casewhere the missing number of times for the reference point C, I LostC,does not exceed the threshold value T1, the procedure proceeds to stepS78 to effect a missing processing for the reference point D.

It is judged in step S79 whether the missing number of times for thereference point D, I LostD, exceeds the threshold value T1 or not.

If the missing number of times for the reference point D, I LostD, doesnot exceed the threshold value T1, then, the procedure shifts to stepS80 where "1" is added to a value of the number of times in missingsuccessively the reference points C and D, i.e. I LostCD, and then theprocedure proceeds to step S81 where it is judged whether or not thesuccessively missing number of times for a plurality of reference pointsC and D, I LostCD, exceeds the threshold value T2. If the missing numberof times I LostCD does not exceed the threshold value T2, the procedureproceeds to step S68.

If the missing number of times I LostCD exceed the threshold value T2,the procedure proceeds to step S135 where the clutch 20 is disconnected,the engine 19 is stopped, and a fail lamp is flashed.

When it is judged in the step S77 that the missing number of times forthe reference point C, I LostC, has exceeded the threshold value T1, theprocedure shifts to step S82 where "1" is set in a reference point Cmissing flag, and then the procedure proceeds to step S78.

Moreover, in the step S79, when it is judged that the missing number oftimes for the reference point D, I LostD, has exceeded the thresholdvalue T1, the procedure shifts to step S83 where "1" is set in thereference point D missing flag, and then the procedure proceeds to stepS80.

When the judgment in step S75 is "NO", i.e. the case where a value ofthe pole counter is none of "4", "3" and "2", it is considered thatthree successive reference points at three positions have been missed.In this case, the procedure proceeds immediately to step S135 where theclutch 20 is disconnected, the engine 19 is stopped, and a fail lamp isflashed.

When it is judged in the step S62 that the received beam signal is notwithin a range of (θan±θK), the operation proceeds to step S63 where itis judged whether or not the received beam signal is within the range of(θbn±θK).

When it is judged that the received beam signal is detected within arange of (θbn±θK), in other words, the received beam signal is the onederived from the reflected light from the reference point B, theprocedure proceeds to step S84 where it is judged whether the value ofthe pole counter is "1" or not. When the judgment in step S84 is "NO",the procedure proceeds to step S87, whilst it proceeds to step S85 incase where the judgment is "YES". Thereafter, the processings for stepS86 as well as steps S88-S100 are carried out.

When the judgment in step S63 is "NO", the procedure proceeds to stepS64 where it is judged whether or not the received beam signal isdetected within a range of (θcn±θK).

When it is judged that the received beam signal is detected within therange of (θcn±θK), i.e. the received beam signal is the one derived fromthe reflected light from the reference point C, the procedure proceedsto step S101 where it is judged whether a value of the pole counter is"2" or not. When the judgment therein is "NO", the procedure proceeds tostep S104, whilst it proceeds to step S102 if the judgment therein is"YES". Thereafter, the processings for step S103 or steps S105-S117 areeffected.

When the judgment in step S64 is "NO", the procedure proceeds to stepS65 where it is judged whether or not the received beam signal isdetected within the range of (θdn±θK). When the received beam signal isdetected within the range of (θdn±θK), i.e. the received beam signal isthe one derived from the reflected light from the reference point D, theprocedure proceeds to step S118 where it is judged whether the value ofthe pole counter is "3" or not.

If the judgment is "NO", the procedure proceeds to step S121, whilst itproceeds to step S119 when the judgment is "YES". Thereafter, theprocessings for step S120 or steps S122-S134 are carried out.

When all the judgments in the steps S62, S63, S64 and S65 are "NO", thereceived light beam is none of the reflected light from the referencepoints A, B, C and D, and as a result it is considered that the receivedbeam signal is either a signal induced by the reflected light from theother reflecting bodies than the reference points or a signal as aresult of receiving the light from an irrelevant beam source so thatsuch beam signal is processed as noise.

When it is judged the received beam signal is noise, the operationproceeds from the step S65 to the step S66 and hence, a noise warninglamp is lit, and the coordinates of the moving vehicle 1 at the timewhen the noise was detected as well as the azimuth of that noise sourceviewed from the moving vehicle 1 are read in and the values thereof arestored in the noise storing means 29.

As shown in the flowchart of FIG. 4, the present embodiment is soconstructed that when each of the reference points A, B, C and D hasbeen missed over the number of times as to the threshold value T1, "1"is set in a corresponding one of the reference point missing flags. Whena state of any one of the reference point missing flags is "1", theswitching means 36 is switched to the side shown in FIG. 1 so that theposition and the advance direction of the moving vehicle 1 arecalculated on the basis of positional informations, differentialazimuths and azimuth angles of the remaining three reference points, andin the reverse calculation means 12, the azimuth of the missingreference point is calculated.

It is to be noted that since processings in the steps S85-S100,S102-S117, and S119-S134 are carried out in the same manner as that ofthe above-mentioned steps S68-S83, the detailed explanation therefor isomitted.

Now, a detailed description is provided of the method for calculatingthe azimuth of a missing reference point, which is performed in themissing reference point reverse calculation means 12. FIG. 5 is aflowchart for making a judgment as to which one of the reference pointsA, B, C and D has been missed and calculating the azimuth of the missingreference point.

In FIG. 5, in step S20, whether or not the reference point A has beenmissed over a preset number of times T1 is judged by whether or not thereference point A missing flag is "1". If the missing number of timeshas exceeded the preset number of times, the process goes to step S21where the azimuth θa of the reference point A is reversely calculated onthe basis of the known azimuths of the three reference points other thanthe reference point A. The calculation formulas for the reverseoperation will be described later. In step S22, "0" is set in thereference point missing flag.

If the missing number of times of the reference point A has not exceededthe preset number of times, the process goes to step S23 where it isjudged whether or not the missing number of times for the referencepoint B has exceeded the preset number of times T1 by whether or not thereference point B missing flag is "1".

If the missing number of times has exceeded the preset number of times,the process goes to step S24 where the azimuth θb of the reference pointB is reversely calculated on the basis of the known azimuths of thethree reference points other than the reference point B. In step S25,"0" is set in the reference point B missing flag.

If the missing number of times of the reference point B has not exceededthe preset number of times, the process goes to step S26 where it isjudged whether or not the missing number of times for the referencepoint C has exceeded the preset number of times T1 by whether or not thereference point C missing flag is "1".

If the missing number of times has exceeded the preset number of times,the process goes to step S27 where the azimuth θc of the reference pointC is reversely calculated on the basis of the known azimuths of thethree reference points other than the reference point C. In step S28,"0" is set in the reference point C missing flag.

If the missing numbers of times have not exceeded the preset number oftimes, that is, if any of the reference point A missing flag, referencepoint B missing flag and reference point C missing flag is not "1", itis judged that the reference point D has been missed over the presetnumber of times, and the azimuth θd of the reference point D isreversely calculated on the basis of the known azimuths of the threereference points other than the reference point D in step S29. In stepS30, "0" is set in the reference point D missing flag.

The reverse calculation of the azimuth of the missing reference point iscarried out by the following formulas. The symbols in the followingformulas are as shown in FIG. 9.

As seen from FIG. 9,

    θ1=tan.sup.-1 {(Y-Yc)/(Xc-X)}

    θ2=tan.sup.-1 {(Yd-Y)/(Xd-X)}

    θd=θc+θ1+θ2=θc+tan.sup.-1 {(Y-Yc)/(Xc-X)}+tan.sup.-1 {(Yd-Y)/(Xd-X)}

The calculation formulas for the reference points A, B and C areobtained in a manner similar to the above described formulas, so thedisclosure and description thereof are omitted.

Now, the above described reference point missing processing and thedetermination processing of the azimuths θa-θd of the reference point asviewed from the moving vehicle 1 are described with reference to theflowcharts of FIGS. 6 and 7.

FIG. 6A is a flowchart illustrating the reference point A missingprocessing (step S88) in which since it is judged in the step S87 thatthe reference point A has been missed, "1" is added to the missingnumber of times for the reference point A, I LostA, in step S160.

In step S161, it is judged whether or not the missing number of timesfor the reference point C, I LostC, is "0", in other words, whether ornot the reference point C had been missed. In the case where thereference point C had been missed, the operation shifts to the stepS163, whilst when the reference points C had been missed, this meansmissing of both the reference points C and A so that the procedureproceeds to step S162 to add "1" to the missing number of times for theadjoining reference points C and A, I LostBD.

In step S163, a difference {θan-(θan-1)} between a pair of the azimuthsof the reference point A which have been detected in the last detectioncycle and the current detection cycle are read as Δθ, so that theazimuths θan-1 detected in the before-last detection cycle and θandetected in the last detection cycle are renewed by the θan and(θan+Δθ), respectively. The difference Δθ between the aforesaid azimuthsis not limited to a result obtained by calculating {θan-(θan-1)}, but afixed value which has been set previously based on a value found by anexperiment may be used as Δθ.

When a particular reference point can not be detected within an expectedrange, the azimuth data of the particular reference point are presumedand renewed by the missing processing as described above on the basis ofthe azimuth data in the last and the before-last detection cycles, andthen the current position and the advance direction of the movingvehicle 1 are calculated on the basis of the renewed data.

Missing processings for other reference points B, C and D are alsosimilarly effected as for the reference point A as seen in FIGS. 6B-6D.

FIG. 7A is a flowchart showing in detail the step S68 (FIG. 4) fordetermination of the azimuth θa of the reference point A.

In step S150, "0" is set as the missing number of times of the referencepoint A, I LostA, in the missing number of times counter 30, and at thesame time, "0's" are set as the number of times I LostAB, I LostDA, ILostAC and I LostCA in the plural missing number of times counter 31,respectively. In step S151, the azimuths θan detected in the lastdetection cycle and θx detected in the current detection cycle are readin as θan-1 and θan, respectively, to renew the data.

In step S152, "0" is set to the reference point A missing flag.

If "0" is set in the reference point A missing flag, the switching means36 is switched to the opposite side in FIG. 1, and the position andadvance direction of the moving vehicle 1 are operated by a firstoperation means 34.

The azimuth θa of the reference point A is determined as describedabove. Processings for determining the azimuths θb, θc and θd of thereference points B, C and D are shown in FIGS. 7B-7D, respectively.Since the procedures for these processings are the same as that of theprocessing for determining the azimuth θa of the reference point A, theexplanation therefor will be omitted.

In accordance with the present embodiment, as described above, whenlight is detected by the beam receiver 3, it is discriminated whether ornot the light is the one which is reflected by one of the reflectors6a-6d located at the predictive reference points. In only the case wherethe light is the relevant one reflected by one of the expectedreflectors 6, the position and the advance direction of the movingvehicle 1 are calculated on the basis of the beam signal received.

In case the light reflected by the particular reflector is not receivedand the particular reference point has been lost, the azimuth of theparticular reference point lost is presumed on the basis of the azimuthsat which the beam signals had been detected in the last and thebeforelast detection cycles, respectively, and the position as well asthe advance direction of the moving vehicle 1 are calculated inaccordance with the data on the presumed reference points. However, whenthe successively missing number of times for one particular referencepoint is more than the predetermined number of times, the position ofthe moving vehicle 1 is detected based on the informations of the threereference points other than the particular missing reference point,whereby steering control for the moving vehicle 1 can be continued.

Simultaneously, based on the coordinate values and azimuths of the threereference points other than the missing reference point, the azimuth ofthe missing reference point is reversely calculated. The azimuthcalculated by the reverse operation is based on the azimuths andcoordinate values of the definite three reference points, and thedetection accuracy is high, different from mere estimation azimuth.

Furthermore, when two reference points are successively missed, it ispresumed that there is a serious trouble so that travel of the movingvehicle 1 is allowed to stop at the time when the missing number oftimes has exceeded a prescribed number of times.

Moreover, while the moving vehicle 1 is adapted to stop at once in thecase where it is judged that three reference points have been missed inthe present example, it may be arranged alternatively in such that apredetermined number of times has been previously set for the case wherethree reference points has been successively missed, and then the movingvehicle 1 is allowed to stop after the missing number of times hasexceeded the predetermined number of times.

As described above, according to the present embodiment, even if thereflected light from a reference point is not normally detected becauseof a tentative trouble, travel of the moving vehicle 1 can be continuedalong a prescribed traveling course by presuming of the position of suchreference point.

When the successively missing number of times for a particular referencepoint reaches such number of times based on which normal steeringcontrol cannot be expected as a result of accumulating errors inpresumption of the reference points, in other words, when such missingnumber of times exceeds the threshold value T1, the control is effectedon the basis of three reference points so that there is no possibilitythat an error in the detected position of the moving vehicle 1 isincreased.

The accumulated error in the detected position of the moving vehiclebrought by estimating the azimuth of the missing reference point will benullified after the azimuth of the missing reference point is calculatedbased on the known value of azimuths.

On the one hand, when it is judged that the trouble is not tentative,but serious one, in other words, when a plurality of reference pointshave been successively missed, travel of the moving vehicle 1 is allowedto stop in an early stage so that the moving vehicle 1 is adapted to notdeviate from a predetermined course.

While missing processing is effected or the moving vehicle 1 is allowedto stop when the reference point or points have been missed by theprescribed number of times in the present example, such missingprocessing may be effected or the moving vehicle 1 may be stopped in acase where reference point or points have been missed during aprescribed period of time or during the time the moving vehicle 1 hastraveled a predetermined distance.

Furthermore, although the present embodiment is so constructed that whenthe reference point was lost, an azimuth of the reference point lost ispresumed on the basis of the azimuths which have been obtained bydetecting beam signals received in the last and the before-lastdetection cycles, respectively, the position and the advance directionof the moving vehicle 1 are calculated in accordance with the presumedreference point, and the steering of the vehicle is conducted before thenumber of missing times reaches the predetermined number, it may be soconstructed that the azimuth is presumed, thereafter the presumedazimuth is used only for the detection of the reference point in thenext cycle, and travel of the vehicle is continued in the same advancedirection as in the last cycle without any modification.

While the moving vehicle 1 has been adapted, in the present embodiment,to be driven by the radio control or the like from a returning positionR to a starting position for working, it may be so constructed that thelight beam is scanned during the time the moving vehicle 1 stays at thereturning position R to detect the azimuths of the reference points, anda traveling course extending from the returning position R to thestarting position for working is operated on the basis of the detectedazimuths, whereby the moving vehicle 1 is allowed to travel to thestarting position for working along the operated traveling course. Inthis case, it is preferably to perform the discrimination process of thereference points during traveling from the returning position to thestarting position for working.

Although the present embodiment is the one in which the presentinvention has been applied to a system wherein the position and theadvance direction of the moving vehicle 1 are detected on the basis offour reference points thereby effecting steering control, the presentinvention is not limited thereto, but is applicable also to a systemwherein reference points positioned at the apexes of a trianglesurrounding the moving vehicle 1 are detected among four referencepoints, the position and the advance direction of the moving vehicle 1are detected on the basis of the positional information on the abovethree reference points thereby effecting steering control, and suchsystem is described in the U.S. patent application Ser. No. 413,934(Japanese patent application No. 63-262191).

More specifically, the system according to the present invention may beso constructed that when one reference point has been missed, theposition and the advance direction of the moving vehicle 1 are detectedon the basis of three reference points which are not limited to thereference points positioned at the apexes of a triangle surrounding themoving vehicle 1 among four reference points, but the other threereference points than that having missed, whereby steering control ofthe moving vehicle 1 is carried out.

As is apparent from the above description, the following advantages canbe attained in accordance with the present invention.

(1) if the number of times for particular one reference point has beenmissed increases, the azimuth of the missing reference point iscalculated on the basis of the known azimuths of the remaining referencepoints other than the missing one, so that, different from estimatingthe azimuth of the reference point on the basis of the reference pointsdetected in the last and before-last cycles, estimation can be made moreaccurately and the re-detectability of the missing reference pointincreases.

(2) When having missed one reference point, since steering control forthe moving vehicle can be continued on the basis of not presumption ofthe missed reference point but the other three reference points thanthat missed, precision in detecting the postion of the moving vehicle isincreased as compared with the presumption of the missed referencepoint.

(3) Since it may be adapted to stop the moving vehicle only when aplurality of reference points were frequently missed, there is nouseless interruption of working so that its working efficiency isimproved.

(4) In case of missing tentatively one particular reference point,traveling of the moving vehicle can be continued by the control based onthe remaining three reference points, whilst when the missed referencepoint can be again detected, the moving vehicle control may be switchedto that based on the four reference points, whereby the moving vehiclemay be traveled as before. Thus, the position of the moving vehicle canbe accurately detected even in a working area under such a poorcondition that the moving vehicle is somewhat rolled, so that anapplicable range can be expanded for moving vehicles.

What is claimed is:
 1. A position detecting system for a moving vehiclewherein a position of the moving vehicle is detected on the basis ofreceived light beam signals from light-emitting means disposed at atleast four reference points, the system comprising:a light-receivingmeans carried on the moving vehicle for rotation in the horizontaldirection for receiving the light beam signals, a means for detectingthe azimuth of each light-emitting means with respect to the movingvehicle on the basis of light receiving intervals in the light-receivingmeans, a means for predicting the direction of the light-emitting meansto be detected in the next scanning on the basis of the azimuthsdetected in the azimuth detecting means, a means for calculating theposition of the moving vehicle on the basis of the detected azimuths ifthe detected position of the light-emitting means is in the directionpredicted in the predicting means, and a means for calculating theazimuth of the undetected light-emitting means on the basis of thepositions of the remaining light-emitting means other than theundetected light-emitting means if the detected position of thelight-emitting means is out of the direction predicted in the predictingmeans, and for predicting the azimuth at which the undetectedlight-emitting means is to be detected in the next scanning.
 2. Aposition detecting system for a moving vehicle as claimed in claim 1further comprising a light radiation means installed rotatably togetherwith the light-receiving means on the moving vehicle, the light-emittingmeans disposed at fixed reference points being replaced withlight-reflecting means which reflect the light radiated from the lightradiation means in the incident direction thereof.
 3. A positiondetecting system for a moving vehicle wherein a position of the movingvehicle is detected on the basis of received light beam signals fromlight-emitting means disposed at at least four reference points, thesystem comprising:a light-receiving means carried on the moving vehiclefor rotation in the horizontal direction for receiving the light beamsignals, a means for detecting the azimuth of each light-emitting meanswith respect to the moving vehicle on the basis of light receivingintervals in the light-receiving means, a means for predicting thedirection of the light-emitting means to be detected in the nextscanning on the basis of the azimuths detected in the azimuth detectingmeans, a first operation means for calculating the position of themoving vehicle on the basis of the positional information and theazimuths of the light-emitting means disposed at at least four referencepoints, a second operation means for calculating the position of themoving vehicle on the basis of the positional information and theazimuths of any three of the at least four light-emitting means, adiscrimination processing means for outputting a reference point-missingsignal when the light beam signal from one of the light-emitting meansis not detected, a switching means responsive to the missing signal forselecting the position of the moving vehicle calculated in the secondoperation means, and a means responsive to the missing signal forcalculating the azimuth of the undetected light-emitting means on thebasis of the positions of the remaining light-emitting means other thanthe undetected light-emitting means and for predicting, on the basis ofthe calculated azimuth value, the azimuth at which the undetectedlight-emitting means is to be detected in the next scanning.
 4. Aposition detecting system for a moving vehicle as claimed in claim 3wherein the first operating means operates the position of the movingvehicle on the basis of the azimuths of the four light-emitting means,differential azimuths defined between two pairs of light-emitting meanspositioned diagonally with each other among the four light-emittingmeans, and the positional information of the four light-emitting means.5. A position detecting system for a moving vehicle as claimed in claim3 wherein the first operating means operates the position of the movingvehicle on the basis of the azimuths of three light-emitting meanspositioned at the apexes of a triangle surrounding the moving vehicleamong the four light-emitting means, the differential azimuths betweenthe adjoining two light-emitting means viewed from the moving vehicle,and the positional information of the three light-emitting means.